Automatic telephone high-frequency trunk



March 1 1927.

s. B. WILLIAMS, JR., ET AL AUTOMATIC TELEPHONE HIGH FREQUENCY TRUNK Original Filed April 1. 1920 8 Sheets-Shet 1 ,R a n MUN 1 619 228 March 1 1927. ET AL .auwomuc TELEPHONE HIGH FREQUENCY TRUNK s. B. WILLIAMS, JR,

Original Filed April. *8 Sheets-Sheet 2 1,619,228 March 1 1927 -s. B. WILLIAMS, JR., ET

AUTOMATIC TELEPHONE HIGH FREQUENCY TRUNK Original Filed April 1. 1920 8 Sheets-Shet 5 /nvenlon5: w o Jamue/ 5 l V/mhms-k/g Lewis M C/emen/f r March 1 1927.

S. B. WILLIAMS. JR.,

AUTOMATIC TELEPH ONE HIGH FREQUENCY TRUNK Original Filed April 1. 1920 8'Sheets-Sheet 4 m f" H Q A- A: 415- (0 E r 1 I I I I I I l l l l I l i I I k I I I I I I k I I I I I' I l I i I I l I I I l l l I l 1 I I l .8, I my I I L J T II II (I K "J Y R by gag/ My March 1, 1927. 1,619,228

5. B. WILLIAMS, JR., ET AL AUTOMATIC-TELEPHONE HIGH FREQUENCY TRUNK Original Filed April 1. 1920 a shet's-sheet' 5 m L: M

mvenforss Jamue/ B. l V/W/ams, Jr. Lew/'5 M C/ememf by filly/ ,4/0'4 1,619,228 March 1 1927' s. B. WILLIAMS, JR. ET

AUTOMATIC TELEPHONE HIGH FREQUENCY TRUNK Original Filed April 1. 1920 8 Sheets-Sheet 6 F/g/ F/qJ H95 F/y7 f/gz F/ 4 F176 H95 //7 venfom: Jamue/ B l V/l/iams J/I Lew/l? M- C /emen/.

1,619,228 March 1 1927" s. B. WILLIAMS, JR; ET AL AUTOMATIC TELEPHONE HIGH FREQUENCY TRUNK Original Filed April 1. 1920 a sheets-sheet '7 5 I w mil Hi k1? 139 (Q0 I a March 1 1927.

S. B. WILLIAMS, JR., ET AL AUTOMATIC TELEPHONE HIGH FREQUENCY TRUNK Filed April 8 Sheets-Sheet 8 lm en fans Jamue/ 5 lt fl/l dms, d/r

Lew/ls M C/emenf 3 or: to any atented at; i, in"; y

saucer. n. wrnnrms, an",

MOUNTAIN LAKES, NEW JERSEY,

or BROOKLYN, New Yo AND Lewis at. onnui NT, or."

AssreNons To wns'rnnN nLnoTmo comm,

INCORPORATED, 015' NEW YORK, N. Y., A. CQRPOTIGN 0E YORK.

AUTOMATIC TnnnrnoNn men -resonan TnUNn.

Application filed April 1, 1920, Serial it'o. 37 0,476. Renewed December 18, 1925.

vThis invention relates to an improved communicating system, and its principal object is to provide means. for controlling switching mechanism and establishing communicating circuits through the medium of high frequency oscillations either transmitted through space in the form of electromagnetic waves or guided upon metallic conductors. y

, It is the object of this invention to pro vide a system in which high fre uency waves may be used as the medium or establishingcommunication between any high frequency station. and any other high fre= quency station of a number of associated stations and as the medium for controlling the operation of switching mechanism at the distant station; in which automatic switch ing mechanism associated with one high fre--- quency station may be operated 'to place that high frequency station in operative relationfwith any one of a number of other high frequency stations; in which the calling high frequency station may have associated withit a number of local stations, which may be subscribers telephone stations, with means under the control of each local station for extending itstcircuit to the associated high frequency trunk; in which two or more high frequency stations may be available for extending a connection from one of an associated group of local stations; in which the automatic switching mechanism and high frequency station selecting mechanism of the calling high frequency station may be under the I control of any local station that has extendthe other high frequency stations; in whichf the distant orcalled high frequency station with switching mechanism.

', for connecting it with any o'neof a n ed its circuit to the'calling high frequency station, so that't-he local station may establish operative relation through the asso ciated high frequency station with any of may be provided ,ber of associated local stations; in which this switching mechanism of the called high frequency station may be under the control of controlling mechanism at thecalling high frequency station, which controlling mechanism at the calling the 7 local station that municatin high frequency station may in turn be under the control of'com trolling apparatus at has become connected with the calling high frequency station, so that the local stahigh frequency stations, and maythen select and establish operative relation with any of the local stations associated with the selected or called high frequency station; in which the callin local station may control the release at oth high frequency stations; in which the calling high frequency station may be prevented from establishing comor controlling relation with a called hig frequency station that is at the time in nunica-tion, either as a calling station or as a called station; Withsome other high frequency propriated by stations preparatory to being used to establish communication with some other high frequency station; in which any local station maybe prevented from extending its circuit to the associated high frequency station if that station has been appropriated by some other .local station; in which a called high frequency station is caused automatically to signal its accessible condition back to the calling high frequency station; in which the receiptof this signal by the calling high frequency, station automatically brings about the operation of apparatus for completingtheconnection of the calling station with the called station, and in which the failure of such signal to. be received prevents the apparatus ofthe calling station from completing the connection; in which.

the unavailable condition of the called high frequency station brings-about the application of a busy signal to the circuit of the calling high frequencystation; in which the impulses for effecting the control of the selecting and connecting switches 'at the.

called high frequency station may be stored up in register apparatus at the calling high frequenc station, and may be released by the receipt of the signal from the called high frequency station indicating its non busy or available condition; in which the register mechanism at the calling high frequency station may receive at their normal rate the impulses determined by the o eration of the controlling switch at the statiomor has been apany of its associated local- 'com lete the connection with the desired loca station associated with the called high frmpliency station; in which the register mec anism at the calling and called high frequency stations may automatically interpose a change-over interval between the groups of impulses transmitted; in which carrier waves of different frequencies may be employed as the media for selectively establishing operative relation between each high frequency station and the various other high frequency stations; in which each high frequency station has a normal carrier wave frequency for receiving and a different normal carrier wave frequency for transmitting,

and in which the selection of any desired high fr uency station is accomplished through 1: e medium of automatic switching apparatus that operates to tune the transmitting system of the calling high frequency station to the normal carrier wave frequency of the called station, and the receiving system of the calling high frequency station to the normal transmitting carrier wave frequency of the called station; in which each carrier wave is multiplexed by having applied to it one intermediate frequency for talkin or communicating and another interme iate fre uency for si nalin or controlling, the 31st intermediate frequency being modulated by the talking or communicating currents and the second intermediate fre uency being modulated by the operation of t e signaling or controlling apparatus; in which the receiving antenna system of each high frequency station is arranged to respond selectively to the two su erpoi'ed intermediate frequencies and uti ize one for the reproduction of the transmitted voice or communicating currents and the other for the reproduction of the transmitted signalling or controlling currents; and in which the circuit organization of each of the high frequency stations is so arranged that the circuit operates as a two-way trunk, and

is automatically adapted for outgoing calls originating in the associated local stations, or for incoming calls originating in local stations associated with other high frequency stations. The foregoing are some of the principal objects that the system of the present invention is designed to attain. The manner in which the foregoin and other desirable objects are accomplis ed will be explained in the following description of the preferred embodiment of the system, and

stations, A, B and C, D, respectively. It

will be understood that there may be a plurality of such radio stations or trunks with their associated local stations. As the other radio stations may all be equipped similarly to those illustrated, it is not necessary to show them, and the stations S1 and S-3 may be assumed to be representative of the other stations. Furthermore, in order to simplify the drawing, the organizations of the two radio stations illustrated are not shown in their entirety. As each of the radio station circuits is designed and adapted to o erate as a two-way trunk, it is equipped with all of the apparatus required for enabling it to be used both for incoming and outgoin connections; and as it is assumed for t e purposes of the present description that station S1 is the calling station and station S3 is the called station, certain of the apparatus at each station that is involved only when the conditions are reversed, or is involved under the conditions here assumed but is fully illustrated in connection with the organization of the other station, is omitted from the drawin or is partially indicated in areas bounded by broken lines. In the complete organization the apparatus and wiring fully shown at either of the radio stations illustrated, is also present at the other station.

Referring now to the organization as it is illustrated at the two stations S-1 and S3, each of the radio trunks is provided with a radio terminal consisting of the antennae, T-1 and R1 (or T3 and R-3) and also with certain conductive terminals, such as the spring jack 55, the passive terminals of automatic switches such as the selector switch indicated at 6, and the active terminals of a line switch 'as indi cated at 16. At the spring jack terminals 55 of the radio trunk the connecting cord' increase may be connected to an automatic system through the inedium'of an operators cordcircuit, such as that shown having associated with it automatic switch-controlling means. The former type is called a full automatic system and the latter type a semiautomatic system. The present invention s equally well adapt-ed to be used in connectionwith either a full automatic or a semiautomatic system and has been illustrated as having the necessary connections for both types. When the radio trunk is being used as an out-going trunk for calls originating in the associated local stations, as A, B, the local lines are connected with it through the medium of line switch and the selector switch 6. The line switch 5 may be of the type commonly known as the Keith line switch, and the selector switch (imay be a selector switch of the Strowger type, the associated circuits for the controlof these switches being of the sort ordinarily used; or any other of the well-known arrangements used in the telephone art for extending the connection of a telephone lineto the central office apparatus may be sub' tituted.

When the radio trunk is used as an incoming trunk for the extension to one of the local lines of a call originating at some other radio station. the circuit of the trunk is extended through the medium of a line switch 16, a

selector switch 17 and a connector switch- 18, these switches being conveniently of the type and having the wiring arrangement of the switches referred to above.

The radio terminal of the trunk may consist of two antennas T-1 and lit-1. These antennae may be of any desired form, and should preferably'be located at a sufiicient distance apart to insure the selectivity of the receiving antenna. with respect-to the energy in the wave radiated by the transmitting an-- 'tenna; or, if it is desired to locate the antennae closer together the irresponsiveness-of the receiving antenna to the energy it receives from the transmitting antenna may be attained by any of the several methods that are available in the art.

The medium that is employed in the present instance for eifecting radio communication between the transmitting antenna T-'1 and the receiving antenna, as R-8, of the distant radio station is a high frequency carrier wave, the oscillatory current for produc ing which is generated in the high frequency oscillator 101.- The oscillator circuit may be of a well-known type comprising a vacuumv tube or thermionic amplifier with an oscillation circuit includ ng inductively related indutances in the input and output circuits of the tube. The filament current for this oscillator is supplied by the filament current battery 9.5, and the plate current is supplied by the plate current battery 96.

-The carrier wave produced by the high frequency oscillator 101 carries two intermemediate frequencies, one of these interme diate frequencies being generated by the oscillator 109 and the other being generated by ,70

the oscillator 145. Both of these are vacuum tube oscillators having oscillation circuits of the same type as the carrier wave frequency oscillator 101 referred to above. The intermediate frequency oscillatory currents gen-. 'erated by the oscillator 109 are modulated by the voice currents transmitted from the telephone transmitter of the associated local station. The voice currents from the associated local station pass over the talking conductors46 and 47 of the trunk and through the four equal windings of the two-way repeating coil 87 into the balancing network 88. The junction points of the two serially included repeating coil windings in each side of the line circuit are connected by way'of conductors 7 8 and 79 with the input circuit of a thermionic amplifier 107, and the out put circuit of the amplifier is inductively coupled with the input circuit of the modulator 108. The operation of the oscillating and modulating-circuits herein disclosed is briefly as follows: The oscillator 109 and modulator 108 are supplied with plate current through the choke coil 97. which has sufficiently large inductance to prevent the passage therethrough of current fluctuations of frequencies as-high as those used in transmission of speech. The plate current supply circuit for theoscillator 109 contains also a choke coil 128 which transmits voice frequencies but has suflicient inductance to prevent the passage of current fluctuations corresponding to the frequency of oscillator 109. Since the current supplied to the tubes 108 and 109 together in parallel is'maintained tube 108 alone is controlled by the impressed voice current, the current through the oscillator 109 is made to vary in a complemental manner and, therefore, the amplitude of the wave generated by the oscillator 109.varies in accordance with voice received over the line conductors. The frequency of oscillator 109 is controlled by the condenser C while the condenser G which is too large to have an appreciable effect on the period of the oscillator, serves to prevent short-circuiting of the battery 96.

The oscillators 109. and 101 are all connected to and feed into the input circuit of the modulating tube 102. Condenser C affords a high-frequency by-pass for the radio frequency current from oscillator 1.01.

The output coils from oscillators 109 and 145 are in series. 1 However, the coupling of the oscillator circuits to the common work circuit'may be made sufiiciently loose to prevent reaction of one oscillator upon another and to prevent the constants of the work circuit from affecting the period of the oscillators.

The action of the modulator 102 is somewhat different from that of 108 since all of the waves are impressed uponthe grid circuit and the modulating action depends upon the variation of the tube impedance to the passage of the radio frequency current under control of the currents impressed from oscillators 109 and 145. The result is that the radio frequency wave is modulated by each of the waves from the intermediate frequency oscillators each of which is, in turn, i'uodulated or controlled by currents or waves of lower frequencies, the one by voice frequency waves, as has been explained, and the other by control impulses as will now be described.

The operation of the intermediate frequency oscillator 145 is controlled at the contacts of the relay 98, which relay is goierned in its operation by the controlling apparatus of the trunk circuit. \Vhen the relay 98 is operated, the oscillator 145 acts to generate oscillatory currents of the fr uency' redetermined by the adjustment 0 the in uctance and capacity of its oscillating system; and when the relay 98 is inert, the oscillator ceases to generate these oscillatory currents.

The output circuit of the modulator 102 is ind-uctivel coupled with the tuned input circuit 104 o a power amplifier 105 of the thermionic type, and the output circuit of the amplifier is inductively coupled with the tuned transmitting antenna T1 of the system. The tuning of the am lifier input circuit 104 and of the transmitting antenna T-1, as well as of the oscillating circuit of the carrier wave oscillator 101 is accomplished through the medium of a plurality of branches under the control of the relays 114,115, 116, and 117; 124,125,126 and 127; and 134, 135 136 and 137. The tuning branches of the carrier frequency oscillator 101 and of the amplifier 105 controlled by the relays 114, 115, 116, 117, and 124, 125, 126, 127, respectively, include condensers; and the tuning branches of the transmitting antenna T-1 controlled by the relays 134, 135, 136, 137 include tuning inductances. It is obvious that while inductanccs areshown for purpose of tuning condensers or both inductances and condensers might be provided where only a variable inductance is shown, and that they might be controlled by relays in the same manner as are the inductances. The capacities of the condensers and the tuning inductances are made variable so that they may be adjusted to produce the desired tuning effects in the associated circuits. The tuning effects are so regulated that when the relays 114, 124, 134, are operated a carrier wave of a certain frequency is propagated from the transmitting antenna T-1, when the relays 115, 125, and 135 are operated a carrier wave of a different frequency is sent out; and in the same way for the other two sets of relays 116, 126, 136, and 117, 127, 137, each of which when operated causes another and different frequency of carrier wave to be transmitted. Each of the four sets of relays may be selected for energization at the contacts associated with the wiper 21 of the station-selecting switch 20 of the trunk circuit; and the wi er 22 of this switch corres ondingly selects or energization an one 0 four relays 154, 155, 156, and 15 which control tuning branches of the receiving antenna R-1 of the station.

The radio receiving system of the station may be understood by reference to Fig. 5, which shows fully the radio receiving system of the station 8-3, the circuit or anization of which is exactly the same as t at of the station 8-1. The receiving antenna, as R-3, is inductively coupled with the tuned input circuit of a thermionic detector 147, and the tuning branches are under the control of relays 154, 155, 156, and 157, which in turn are controlled by means of the conductors extending to the contacts associated with wiper 22 of the station-selecting switch 20. The branches controlled by the relays 154, 155, 156 and 157 contain condensers the capacity of which is adjusted and set so that when any one of the branches is closed the receiving system is made responsive to a particular one of the carrier wave frequencies with which the system is designed to cooperate. The output circuit of the detector 147 includes serially the two frequency filters 148 and 149; and also has bridged across the filament and plate circuit a condenser for eliminating the unmodulated carrier frequency. The filter 148 has its constants so adjusted as to select the signaling intermediate frequency and to pass the talking intermediate frequency, and the filter 149 is adjusted to select the talking intermediate frequency and to pass the signaling intermediate frequency. The filter 149 is inductively coupled with the input circuit of the detector 162, and the output circuit of the detector 162 is inductively coupled with the input circuit of the amplifier 163. The output circuit of the amplifier is inductively cou led with a circuit including two windings o the twoway repeating coil 87. The inductive relation of these two windings with the other windings of the repeating coil 87 is such that the voice currents flowing in the circuit of the conductors 74 and 75 are repeated into the trunk talking conductors 46 and 47 connected with the other windings of the repeating coil, but are not repeated into the branch connection witlrthe am lifier 107 of the station of Fig. 6 by way 0 the conductors 7 8 and 79. As a result of this arrangement, which is well-known in the art, the

voice current modulations that reach the called station through its receiving antenna are prevented from re-acting upon the radio transmitting system of that station and cans ing similar voice current modulations of the oscillatory currentspassing to its transmitting antenna.

The filter 148 which selects the signalling intermediate frequency of the received oscillation is inductively coupled with the input circuit of the thermionic detector 151, and the output circuit of this detector is inductively coupled with the input circuit of the amplifier 153, the output circuit of which in turn is inductively coupled with the circuit of the rectifier 159. The circuit of the rectifier includes the winding of relay 99, and this relay acts through the medium of conductor 80 to govern the operation of certain switching mechanism of the associated trunk. t

The apparatus which is used to transmit and receive by means of any one high. frequency wave as distinguished from that which is used only when a wave of a different frequency is employed, is commonly known as a channel or a high frequency communication channel. It will be seen that each terminal apparatus is capable of transmitting or receiving through any one of a number of channels and thatone such channel may be selected and appropriated for use by a pair of stations, to the exclusion of all other stations of the system and that the channels, by virtue of the different frequencies which they employ respectively, do not interfere with one another, but enable independent simultaneous communication between difierent stations of the system.

Each of the radio stations is normally tuned to utilize two carrier wave frequencies, the transmitting system being tuned to transmit one carrier wave frequency and the receiving system .being tuned to respond to another carrier wave frequency. These pairs of frequencies are different for each of the radio stations of the system. When a call is received by any of the stations it is received at the carrier wave frequency that is normal to the receiving system of that station, and underthese circumstances the carrier wave that is transmitted from the transmitting system of the called station is the frequency that is normal for that transmitting system. When any of the radio stations p is calling another. station, the associated switching apparatus is operated to tune the transmitting system of the calling station to the carrier wave frequency to which the called station normally responds, and to tune the receiving system of the calling stationto the carrier wave frequency that the called station normally transmits. For example,

the carrier wave length that four radio stations may normally be. tuned to transmit and receive may be as follows:

Thus, for instance, in the above arran ement, if radio station S1 is calling ra io station S-3, station S- 1 operates its switches to tune its transmitting system to a wave length of 425, which is the wave length to which the receiving system of station S3 normally responds; and to tune the receiving system of station S-l to a wave length of 350, which is the wave length that station S-3 normally transmits. If radio station S-3 were the calling station and station 8-1 were the calledstation, then station S3 would adjust its transmitting system to the wave length 150 to which the receiving system" of station 8-]. normally I responds, and its receiving system to the wave length 160 which station S-l normally transmits. In like manner any radio station in calling any other radio station operates its station-selecting switch 20 to change the tuning of its transmitting and receiving systems from their normal wave lengths to the wave lengths of the receiving and transmitting systems respectively of the called station. The switch. 20 thus in effect selectsrthe trunk branch communicatin with the called station. The carrier wave en the referred to in the above table are mere y typical, as any desired combination of noninterfering wave lengths may be employed and noninterfering communication between as many radio stations may be elfected as there are such combinations of wavelengths to which the radio stations may be made selectively responsive. a

The tuning of the transmitting s stem of each station is controlled throu h t emedium of conductors 81, 82, 83 an 84, and the tuningof the receiving system of each station is controlled through the medium of conductors 91, 92, 93 and 94. At each of' the radio stations the particular conductors of these two groups that control the tuning of that station to its normal transmittingand receiving wave lengths are not extended to the corresponding contact points of the wipers 21 and 22 of the associated-station-- selecting switch 20, but instead are extended to other contacts of theswitching apparatus that are closed when the associated station is -receiving a call from some other station. Thus, in the case of station S-1 the conductor 91 of the receiving system tuning group is not extended to the'first contact point of the wiper 22 of the station-selecting switch, but is normally closed through the medium .of contact 27 of the station-selecting switch and a back contact of the relay 12, so that normally the receiving system is tuned to the frequency to which the radio station Sl is adapted to respond. Likewise the conductor 81 of the transmitting s stem tuning grou is not connected with the first contact 0 the wlper 21 of the station selecting switch, but is ex-.

" are disconnected from the station-selecting switch and have normal connections as described above.

As has been stated, each carrier wave in the embodiment of the system disclosed carries two intermediate radio frequencies, one of which is modulated to carry the speech frequencies and the other, of which is modulated or controlled to carry the signalling and controlling impulses. These intermediate frequencies may have any desired value above audio-frequency and low the carrier wave frequency range. For example, the talking intermediate frequency may be 20,000 and the signalling intermediate frequency may be 50,000. The talking and signalling intermediate frequencies may be the same forall of the carrier waves employed, as the non-interference between simultaneously communicating pairs of radio stations is efl'ected by the different carrier wave lengths that are em loyed.

Each of the radio trunks lias associated with it a receiving register switch 100 and a transmitting register switch 150, employed when the associated radio station is calling another radio station; and a receiving register switch 200 and transmitting register switch 250, emplo ed when the associated radio station is being called by some other radio station. In the present instance these receiving and transmitting register switches are each made up of as many single motion step-by-step switches as there are groups of. impulses in the impulse train, or digits in the number that is being called, together with certain controlling relays. Such stepby-step switches are well known in the art, and need not be particularly described. The movement of the switch wipers of each of these step-by-step switches is effected by means of an associated stepping mag'uel' which is first operated to advance .the wiper to the desired one of its associated contact points; and the return of the switch to nor mal is brought about by further energizations of the stepping magnet which cause row of contact points until it again rests on its normal contact point. This same type of switch is used for the station selecting switch 20 associated with the trunk circuit, and also for the auxiliary switches 190 and 195 associated with the transmitting register switch 150. The associated circuits of these various switches may' be controlled in a series of off-normal contacts operated by cams on'the same shafts that carry the wipers of the switches.

Associated with the trunk in the form herein disclosed, are also a number of plunger relays, as 68, 70, 72, 141 and 142, which are employed to introduce relatively large time intervals into the operation of certain parts of the organization. As indicated, the plungers of these relays are retarded in their inward movement and are permitted to move freely on their return movement. They may be of the type disclosed in the United States Patent No. 1,337,680, granted April 20, 1920, to Williams et al.

Briefly stated the operation'of the particular embodiment of the system here disclosed is as follows: When a subscriber wishes connection with another subscriber whose station must be reached through a radio trunk, the taking of his telephone receiver from its hook causes his line switch to extend the circuit of his line to a selector switch; and this switch is operated in response to. the first transmitted group of impulsesto bring its switch wipers into engagement with the terminals of the first of the radio trunks.

If the first radio trunk is in use, either in' establishing an outgoing connection to some other radio station or in establishing an incoming connection from such a station, there is a busy test potential on the terminals of the trunk, and the selector switch is prevented from making connection with this trunk, and proceeds to the next radio trunk. If the trunk is not in use the selector switch establishes connection with the trunk terminals. The second group of impulses from the calling subscribers station causes the operation of the radio station selector switch associated with the selected radio trunk to connect with a certain one of the sets of associated terminals, depending upon the number of impulses in the second group sent from the calling subscribers line. The cessation of this second or station-selecting group of impulses energizes the selected set of switch terminals and effects a characteristic tuning of the high frequency oscillator, the power amplifier, and the transmitting 'the wiper to continue its movement over the lector switch for antenna of the transmitting system of the radio trunk, this tuning being such as to cause the radio frequency carrier wave applied to the transmitting system to be of the frequency to which the receiving antenna of the called radio station is normally tuned. The receiving antenna of'the calling radio trunk is also, by the same operation, tuned to respond to the carrier wave that the called radio station is normally adapted to apply to its transmitting antenna. As soon as the receiving antenna of the calling radio trunk has been brought into tune with the transmitting antenna of the called radio trunk or station, the calling trunk is in condition to respond to the normal carrier wave of the called trunk. If the called trunk has been called by some other radio trunk, the transmittin antenna of the called trunk is active and 1s sending out its normal or characteristic carrier wave with an intermediate signaling frequency impressed upon it. Therefore, under these circumstances, the receivin calling radio trunk respon s to the carrier wave and intermediate signaling frequency of the called trunk and operates apparatus that applies a busy tone to the cal ing subscribers line and prevents that line from becomin extended to the called radio trunk. But if t e called radio trunk is not at the time receiving a call from some other radio trunk, this busy tone is not a plied; and an instant later apparatus ma e operative a predeterminediune interval after the cessa tion of the second or radio station selecting group of impulses, a plies the selected carrier wave with its ta king and signaling intermediate frequencies and the called radio trunk, responding to the signaling intermediate frequency, applies its own normal carrier wave with the superposed intermediate signaling frequency to its transmitting antenna system, thus making itself unavailable to any other calling radio trunk, and also rendering itself busy to calling ones of its associated lines. At the same time, the called radio trunk, in response to the intermediate signaling frequenc'y applied by the calling trunk, extends its circuit to a sepresently completing connection with the local called line.

Following the second group of impulses, the subsequent impulse groups are applied to the line as were the former groups of impulses'by means of the dial at the calling subscribers station; and each of these groups produces a corresponding displacement'of a corresponding member of a receiving re ister switch associated with the calling ra io trunk. At the end of the last group of impulses the radio trunk operates apparatus to extend the talking conductors of'the trunk tem of the trunk, and also to start the sending, under thecontrol of a transmittin system of the' register to the radio transmitting sys- 0' rec, p b ister switch, of switch controllingradio 1mpulses in accordance with the setting of the receiving register switch of the calling trunk.

But this 0 eration is made dependent upon another usy test that is completed by the calling trunk in the interval between the cessation of the second group of received impulses and the end of the last group of received impulses. This busy test is made to determine whether or not the called radio trunk is in use as the calling station of some other radio connection. If the called radio trunk is thus busy, it follows that its radio station selecting switch has been moved to bring the radio transmitting and receiving system of the called trunk into tune with t e radio trunk that it is calling, and that consequently the receiving antenna of the called radio trunk does not have its normal tuning, and thus is not res onsive to the trunk that is now calling it. Therefore, whenat the termination of the second group of impulses the carrier wave frequency corresponding to the receiving antenna frequency of the called trunk is applied to the transmitting antenna of; the calling trunk, the called trunk does not respond to the superposed intermediate signaling frequency of the carrier Wave, and does not send out over its transmitting antenna the carrier wave to which the receiving antenna of the calling trunk is now tuned. The result of this failure to receive a response from the called radio trunk is that at the end of the last group of impulses the calling radio trunk brings about the application of busy tone 'to the calling subscribers line and prevents the extension of the line to the called trunk. But if during this interval the called trunk is in its normal condition, and responds to its normal frequency as applied by the calling trunk, then the called trunk sends out a return signal that is effective, at the end of the last group of impulses, to bring about the closure of a circuit that starts the transmission of the switch selecting impulses from the-calling radio station and closes the talking conductors at that station.

The transmission of the switch selecting radio impulses from the calling to the called radio station is effected by successively withdrawing the .si nalling intermediate frequency from an app yingit to the carrier wave at the calling station. The radio 'impulses are controlled by the transmitting register switch at the, calling radio station under the control of the associated receiving switch, the apparatus operating to transmit the radio impulses at a rate slower than that atwhich the impulses are received from the calling subscribers station; and the apparatus also operating to separate the groups of radio impulses by change-over intervals. At the called radio station the received radio im ulses produce a corresponding setting the swltch elements of a" 1 radio station and its associated apparatus that is actuated b pulses is operate to send 0 crating impulses to the line selecting switc es at the normal calling rate, a rate faster than that at which the radio impulses are received from the calling radio station.

These registers, if desired, could be made to transmit the radio impulses at the normal calling rate but it is preferred to send them more slowly than switch-controlling rmulscs as normally transmitted over wire lines. One reason for this is to insure a more positive action of the radio-receiving apparatus and to avoid the effects of static For this purpose the relay the radio-controlling imrefera ly made slow-to-respond in any Weli known manner, so that a more or less sustained current is IIGCGSSHIX to eifect its complete operation. The seen in registors are then set to send sufiicient radio impulses to insure the energization of the receiving relafy, but a static impulse being of irregular requency and of com aratively short, duration will not ordinari y be sufiicientl sustained to cause a false opera tion of t e relay. In case the high frequency waves are transmitted over line wires as in the carrier wire systems, this precaution is not so necessary and the sending registers may, therefore, be set to transmit the high frequency control impulses at a greater rate of speed.

These impulses act to build up the connection through the line selecting switches to the called suoscribers line in the usual way. The dis-establishment of the connection is under the control of the calling subscriber at the calling radio station. hen the calling subscriber hangs up his telephone recelver, the circuits at tion controlled by the subscribers switch hook are released and the various switches are returned to normal. The return of the switches to normal withdraws the local busy test from the calling radio trunk, re-establishes the normal tuning of the receiving system of the trunk, and interrupts the carrier wave with its applied intermediate talking and signalling frequencies. The cessation of the received carrier wave and its signalling intermediate frequency at the called radio station releases the radio trunk at that disturbances.

sociated line -tion of the y long b the calling radio stastation and restores the associated relays and switches to normal, thus again rendering the trunk available for transmitting a local originated call or receiving a. call from a distant radio station.

Specifically, the operation of the system is as follows: When the calling subscriber, who may be assumed to be the subscriber at station A or B, takes his telephone from its hook, the resultant operation of the asswitch .5 connects the circuit of the calling line with an idle trunk extending to a first selector switch 6. The means for effecting this operation are well known in the art, and need not be described in detail. The calling subscriber then proceeds to operate his dial 4 to produce the groups of impulses that control the operaautomatic selecting switches. For the purpose of illustration, it'ma be assumed that the terminals of the associated radio trunks arelocated in the first contact level of the first selector switch 6, the terminals of the other levels being connected with trunks extending to second selector switches in the same or other automatic exchanges, in the usual manner. sumption, the calling subscriber, in order to gain access to the terminals of operates his calling dial so as to produce one impulse of current, as a result of which the wipers of the first selector switch 6 are rought in a well-understood way into engagement with the terminals of an idle radio trunk. When the calling line thus seizes the radio trunk, a circuit is closed through the station apparatus and over the conduc tors of the calling line that brings about the energization of the line relay l1. Relay 11 in operating closes a circuit that extends 'rom battery through the winding of slo'w-.

release relay 12, front contact and armature of relay 11, and right-hand back contact-and armature of relay 42 to ground. Relay 12 in operating opens at its outer right-hand armature and back contact the normal en-' ergizing circuit of the relay 154 of the associated receiving tends by way of conductor 91 and normally closed contact 27 of the station selecting switch 20. It is the normal closure of this circuit that maintains the normal tuning of the receiving antenna R-l; therefore the opening of the circuit upon the response of relay 12 immediately changes the tuning of the receiving antenna and makes the assoa radio trunk,

antenna system, which ex-- Upon the above asv ciated station unavailable for receiving calls from other radio stations.

At its left-hand armature and front con-.

tact relay 12 in operating closes a circuit that applies ground to the test terminal of the radio trunk u on the first selector switch 6, thus making t e trunk test busy to other calling local stations. This same groundis applied by way of inner left-hand armature i switch 20 to take one step,

of the radio trunk.

contact 24: armature and front contact path through and back contact of relay 42 and inner lefthand armature and back contact of relay 41 to the winding of rela 40. Relay in operating produces a usy test condition upon the test terminals of the trunk jack Relay 12 in operating also at its inner right-hand armature an front contact partially prepares a path for the transmission of stepping impulses to the stepping magnet 28 of the station selecting switch 20.

Upon the production of the second group of impulses by the operation of the 1al'4 at the calling station, the interruptions of the line circuit cause an intermittent retraction and attraction of the armature of line relay 11. This serves to open and close the energizing circuit of the associated relay 12. But as that relay is of a slow releasin type, it maintains its armatures'attracted uring the intermittent operation of relay 11. The first retraction of the armature of relay 11 closes a circuit that/extends from battery through the winding of stepping magnet 28 of the station selecting switch 20, winding of slow release relay '29, normally closed of switch 20, inner right-hand of relay 12, back contact and armature of relay 11, and righthand back contact and armature of relay 42 ground. This causes the station selecting thus opening the normally closed contact 24; but the operation of relay 29 has closed a locking path for. itself at. its right-hand front contact and armature, in shunt of the path b way of the contacts-24 of switch 20, so t at relay 29 maintains an energizing path for itself and stepping magnet 28:

alternately open and close the energizing the windings of stepping magnet 28 and relay 29 in ser es. Stepping magnet 28 is therefore intermittently operated to cause the advance of the wipers of switch-20; but relay 29, being slow to release, maintains its front contacts closed until, at the end of the group of impulses, the relatively long attraction of the armature of relay 11 opens the energizing circuit of relay 29 long enough to permit it to release. When the relay 29 releases it extends the stepping circuit controlled at back contact and armature'of relay l1 and front contact of relay 12, to the operating: mechanism of the receiving regisier switch 100 by way of right-hand armature and back contact of relay 29 and contact 25 of station switch 20 to control the operation of the receiving register, subsequently be described; and also, left-hand back contact and armature, apphes ground from the outer right-hand armature and front contact'of relay 12 to the wipers 21 and 22 of the station selecting switch The'grounding of wipers 21 and 22 of the three steps an station and attractions of the armature of relay 11 y gized as will at its switch 20 closes a path for the operation of the set of tuning relays that controls the tuning of this radio trunk or station to the radio trunk or station that is being called.

In the present instance, it is assume it is the radio station 5-3 with which the (1 radio station 8-]. associated with the callin line is to be operatively related. This being the case, the wipers 21 and 22 of station selecting switch20 are resting on their third contact oints, that is, they have taken consequently the ground controlled by these wipe-rs is app ing relays 116, 126 and 136 of the transmitting antenna system, and to the relay 156 o the receivin antenna system. The relays 116, 126 an 136 close tuning branches of the high frequency oscillator 101, of the power amplifier 105 and of the transmittingantenna T-1 which give the radio transmitting circuit such characteristics that the .carrier wave a frequency corresponding to the frequency to which the receiving antenna R-3 of radio station 8-3 is normally tuned to respon The operation of relay 156 closes a branch which tunes the receiving antenna R-l to respond to the frequency of carrier wave that the called radio station S3'normally transmits. Therefore, as a result of the movement of wipers 21 and 22 of selecting switch 20'to their third contact position, dueto the impulses relayed from the calling subscribers dial, the transmitting antenna T-l. and the receiving antenna R1 of the associated radio station tively to the receiving antenna R3 and the transmitting antenna T-3 of the called radio As soon as the receiving antenna R1 of station S1 is brought into tune with the transmitting antenna T-3 of station s-h, if the called station S-3 is busy as a result of being in communication with some other station that has called it, the transmitting antenna T-3 of station S--3 will be enerand sending out the normal carrier wave of station S3 upon d that lied to the tunwhich is superthat it produces and transmits has S1 are tuned respecposed an intermediate signaling frequency.

ihe way in which this comes about will be described hereinafter. To this carrier wave from the called radio station S-3, with its superposed intermediate signaling frequency, the receiving antenna system of the calling radio station S-1 is now responsive; and as a result they carrier wave from the called station brings about the energization of relay 99, in a manner hereinafter described. The operation of relay 99 closes a circuit that extends from battery through the winding of busy tone relay 31 (see Fig. 1), outer left-hand back contact and armature of relay 35,

front contact of front contact and armature 20. of relay 60, conductor 80, and armature and eration of that relay antenna system to ground. It should be noted at this oint that the. relay was operated imme 'ately upon the seizure of the radio trunk by the calling line, over a circuit extending from battery through the winding of relay 60, inner right-hand back contact and armature of relay 30, and outer righthand front contact and armature of relay 12 to ground. As a result of the closure of the energizing circuit of busy tone relay 31, relay 31 disconnects the talking conductors 46 and 47 of the radio trunk from their normal extensions to the radio transmitting system of the trunk, and connects them with a source of busy tone current 44, as a result of which busy tone is applied to the calling subscribers line, thus notifying the subscriber that the radio station with which the called line is associated, is busy. Relay 31 in operating also, at its left-hand front contact and armature, closes a locking circuit for itself that extends by way of the outer right-hand back contact and armature of relay 30, and outer right-hand front contact and armature of relay 12 to ground. This insures the maintaine ener ization of relay 31 and the continued app ication of busy tone current until the calling subscriber hangs up and releases rela 12.

The interval'durin WhlCh the busy. tone relay 31 may be energlzedby the response of relay 99 to the carrier wave and signaling frequency of the busy called radio station is but of brief duration. This interval commences at the'instant the receiving antenna system of the callingradio station is brought into tune with the transmitting system of called radio" station uponthe energization of the tuning relays by the release of relay 29, and the breaking of the energizing circuit of busy tone relay31 at outer left-hand back contact and armature of relay 35 by the opupon the release of relay 29. The" operationof relay 35, however, is retarded by the interposition of certain slow relays between the contacts of relay 29 and the energizing circuit of relay 35. When relay 29 first operates, at the beginning of thestation se ecting group of imulses, it closes a circuit which extends from attery through the winding of relay 32, left-:hand front contact and armature of relay 29 and outer right-hand front contact and armature of relay 12 to ground. Relay 32 in operating operates relay 33; and that relay in operating closes a circuit for energizing relay 34 by way of the front contact and armature o relay 33, left-hand back contact and armature of relay 31, outer right-hand back contact and armature of relay 30, and outer right-hand front contact and armature of relay 12 to ground. Relay 34 in operating closes one break in the energizing circuit of relay 35. But there is ancalling -mature of relay 39 other break in this energizing circuit that is not closed until relay 33 releases. At the end of the station selecting group of impulses, the release of relay 29 (which instantly brings the receiving system of the calling radio station S1 into tune with the transmitting system of the called station S3, as has been described), breaks the energizing circuit of relay 32. That relay reeases slowly and breaks the energizing circuit of relay 33. That relay in turn releases slowly and closes at its back contact the second break in the energizing circuit of relay 35 before the first break in that energizing circuit is opened by the slow release of relay 34. Therefore, the operation of relay 35, vhich opens at its outer leftw'hand armature and contact the energizing path to the busy tone relay' 31, lags for a redetermined interval behind the tuning o the calling radio station to the called radio station; and in this interval the operation of the busy tone relay 31 by the response of the relay 99 may take place in case the called radio station is busy.

When the relay 35 operates a moment after the termination of the second group of impulses, it not only closes a lockm ath for itself b way of its inner left-hand f ront contact an armature, but also closes a circuit that extends from battery through the winding relay 89 (Fig. 3), conductor 90, closed contacts 26 of switch 20, outer righthand armature and front contact of relay 35, left-hand back contact and armature of relay 29, and outer right-hand front contact and armature of relay 12 to ground. The operation of relay 89 closes the main leads over which current is supplied from the source of filament current 95 and the source of plate current 96 to the radio transmitting apparatus. Relay 35 in operating also closes a circuit that extends from battery through the winding of relay 98 (see Fig. 3), conductor 85, right-hand front contact and armature of relay 35, and back contact and arto ground. Relay 98 in operating as a result of the closure of this circuit, completes thepath for the application of the plate current to the signaling in termediate frequency oscillator 145. This causes the oscillator 145 to generate currents of an intermediate frequency and to apply them to the circuit of the modulator 102 where they are superposed upon the currents that are being generated by the high frequency carrier wave oscillator 101, and the resultant or component current is passed through the intermediate train of apparatus I to the transmitting antenna T-1, from which the wave is transmitted to the receiv-. ing antennae of the various other radio stations.

As the carrier wave component of the closed contacts quency oscillator the called station S3.

reiaaes 149, the signaling frequency component pass ing through the series of detecting, am-

plif ing and rectifying devices, as has alrea y been described, and causing the operation of the associated relay 99. This relay,

in operating, closes a circuit that extends from battery through the winding of relay 61 (reference now being had to the apparatus at the called radio station S--3), back contact and armature of relay 60, conductor 80, and armature and front contact of relay 99 to ground. Relay 61 inoperating closes at its. right-hand front contact and'armature an energizing circuit for relay 62,, and relay 62 in operating closes a locking circuit for itself by way of its inner right-hand front contact and ar ature and the inner normally 2f the plunger relay 68.

When relay 2 operates it energizes devices to tune the transmitting system of the calledradio station S-3' to its normal carrier wave frequency, for supplying filament station and to close the circuit for applying the intermediate; signaling frequency to the called statibn carrier wave. This is accomplished as follows: The operation of relay 62-a-pplies ground to the conductor 83 for the energization of tuning relays 116, 126 and 136 that are associate respectively with the output circuit of the high fre- 101, the input circuit 104 of the power amp circuit of the transmitting antenna T--3 of These relays in operating close the particular branches of the associated tuning circuits that adapt the radio transmitting apparatus to the production and transmission of a carrier wave having the frequency which is normal to this particular station -S3. In its opera tion relay 62 also closes at its outer left-hand armature and front contact theenergizing ply leads from circuit of relay 63; and relay 63 in operating closes a circuit that extends from battery through the winding of relay 89 (see Fig. 6), conductor 90, and inner righthand front contact and armature of relay 63 to ground. This operates relay 89, which in operating closes the current supthe source 95 of filament current and the source'96 of plate current and causes the production and transmission of S.-3 is normalto close the main leads and plate current to the radio transmitting devices of the called lifier 105, and with the the normal carrier wave with its superposed talking intermediate frequency. Relay 63 in operatin also closes a circuitthat extends from attery throu h the winding of relay 98 associated with t 1e signaling intermediate frequency oscillator 145 of station S3, conductor 85, outer left-hand ar1na ture'and front contact of relay 63, back contact and armatureof relay 39 to ground. Relay 98 in operating completes the circuit for the application of plate current to the associated signaling intermediate frequency oscillator 145, thus causing the signaling intermediate frequency to be superpose upon the carrier wave.

Relay 63 of station S-3 when it operates as a result of the receipt the calling radio station, also closes a circuit that extends from battery through the winding of relay 64, outer right-hand front contact and armature of relay 63 and righthand back contact and armature of relay 66 to ground. Relay 64 in operating closes a circuit that extends through the winding of relay 14 associated with the line switch 16 of the called station radio trunk (see Fig. 7), inner back contact and armature of relay 13, retardation coil 43, armature and front contact of relay 64, left-hand back contact and armature of relay 40, outer left-hand back contact and armature of relay 41, and outer back contact, and armature of relay 13 to ground. Relay 14 in operating energizes the associated relay 13 by way of its left-hand winding, and relay 13 operates the plunger (not shown) which extends the conductors of the radio trunk by way of the line switch 16 to a preselected trunk extending to a first selector switch. When relay 13 operates the line switch 16 it closes a circuit that extends from battery through its righthand winding,'right-hand back contact and armature of relay 41, inner right-hand back contact and armature of relay 40, and the test terminal and corresponding contact of the line switch 16 to ground by way of the test conductor of the trunk-- to the first selector. Closure of this circuit maintains relay 13 energized. Relay 13 in operating disconnects rela of the ra io trunk, disconnects ground from conductor 48 of the trunk, and applies ground by way of outer left-hand armature and front contact of relay 13 for the energization of relay 42. Relay 42 in operating applies battery by way of the outer left-hand front contact and armature of relay 42- and outer right-hand back contact and armature of relay 40 to the test terminal of trunk spring jack to make the trunk test busy at this point. Relay 42 also, at its inner left-hand front contact and armature, applies ground to the test terminal of the radio trunk at the first selector of the signal from 14 from the tallging conductor 49 i switch 6 to make the radio role trunk test busy at this point. It also, at its rigl1thand armature and front contact closes a circuit for energizing relay 30. Relay 30 in operating disconnects the trunk talking conductors 46 and 47 from the branches 56, 57, and 58, 59, over which the local calls have access to the radio trunk, and connects the talking conductors 46 and 47 with the conductors 48 and 49 over which the incoming calls from distant radio stations are'extended through to the local lines associated with the trunk. Relay-30 also at its lefthand armatures and their resting contacts disconnects the ground controlled at the front'contact of relay 12 from conductors extending to various relays that are involved in the operation of the trunk on connection with calls incoming from local lines,-including the conductor extending to 60, which is thus rendered incapable of siiftin the connection of the conductor 80, contro led by relay 99 of the receiving antenna system, from the winding of relay 61 which controls the call-receiving operattion of the radio trunk.

Another function performed by the relay 63 of the called radio station upon the receipt of the radio signal from. the calling station is that of completing the connection of the talking conductors 46 and 47 of the associated trunk with the radio transmitting and receiving apparatus of the trunk. This it does by closing the circuit that extends from battery through the winding of relay 36 (see Fig. 7) and inner left-hand arma ture and front contact of relay 63 to ground. Relay 36 in operating completes the connection of the talking conductors 46 and 47 with the two-way repeating coil 87, and

through it to the radio transmitting and receiving a paratus of the trunk.

From t e foregoin it may be seen that the result of the a p mation of the signaling intermediate iequency to the carrier wave of the calling radio station at the end l of the second group of impulses at the calling station, is to cause the called station to send out its normal frequency carrier wave upon which is superposed the talking and signaling intermediate fr uencies; and to cause the radio trunk of t e called station to close its talking circuit, disconnect the talking circuit from the branches over which local calls may be received and extend the trunk to a first selector trunk, and.

make the local branches of the radio trunk test busy.

Returning now to the operations that are taking place in the circuit ofthe calling radio trunk, the end of the second or station selecting group of impulses brings about the release of relay 29, so that at the retraction of the armature of relaylll at the beginning of the next group of impulses, a circuit is of relay 129,nprma normally closed switch contact 111, conductor 166, contact 25, now closed, of the station selecting switch 20, right-hand back contact and armature of relay 29, inner right-hand front contact and armature of relay 12. back contact and armature of relay 11, and right-hand back contact and armature of re ay 42, to ground. The first impulse opens register switch contact 111; but 1n the meanwhile relay 119 is operated to close an alternate path by way of its lefthand front'contact and armature so that subsequent impulses produced by th tion of the relay 11 pass to the step magnet 118 over this path. constructed as to be slow to release, as a result of which it maintains the circuit of itself and the stepping magnet 118 closed as long as the impulses are passing, and opens it when relay 11 becomes continuously energized at the end of the group. of impulses. For each of the impulses that pass through the stepping' magnet 118, the associated switch wiper 110 moves forward one step, and at theend of the impulses is left resting upon an associated contact corresponding in number to the number of impu ses in the group sent-by the calling ,subscribers station.

When therelay 119 is released at the termination of this group of im ulses it extends the steppingcircuit contro led by relay 11 to thenextxswitch of the receiving register 100, so thatwhen relay 11 next releases at closes a circuit that extends from battery through the. windin of relay 128, windin y closed contact 121 o the second switch, contact 112, now closed of the first switch, left-hand back contact and armature of relay 119, and thence over the path already-traced by wa of contact 25 of the station selecting switc and contacts of relays 29,..12, 11 and 42 to ground. The operation of the apparatus of the second switch'is exactly like that of the first regis ter switch and need not be described in detail. As a-result of this operation, the secand switch advances its wiper 120 to a contact corresponding in number to the number of impulses in the particular group that is being received. At the conclusion of the impulses in this group, the relay 129 of the second switch releases and extends the stepping circuit by way of contact 122, now closed, of the second switch to the operating magnet of the third receiving register e opera- Inn switch. The stepping circuit that is c osed upon the release of relay 11 at the start of the next and last oup of impulses, extends from battery t rough the windings of 

